Japanese aviation authorities said Wednesday they found no evidence of overcharging in a charred lithium-ion battery on the All Nippon Airways Co. Boeing 787 Dreamliner that made an emergency landing last week in Kagawa Prefecture.
The output voltage of the main battery of the Dreamliner was within a normal range, the Japan Transport Safety Board said, based on its analysis of the flight data recorder. The main lithium-ion battery is under the cockpit.
Prior to the finding, excess voltage was suspected as the cause of smoke that appeared inside the ANA jet during its flight to Tokyo on Jan. 16.
The maximum design voltage of the battery, joining up eight lithium-ion cells in a series, is 32 volts, according to the safety board.
The data showed that the voltage stayed at 31 volts for a while during the flight, but later became unstable and eventually fell sharply.
A probe by the U.S. National Transportation Safety Board has found that a lithium-ion battery that caught fire on a Japan Airlines Co. Boeing 787 in Boston earlier this month was also not overcharged, with power output remaining below 32 volts. That battery, in an aft compartment, provided power to an auxiliary power unit.
The Japanese safety board said it will also take CT scans of the ANA jet’s aft battery for its APU, although it is not believed to have had any problem. The smoke came from the main lithium-ion battery under the cockpit.
The purpose of taking the CT scans is to compare data with the main battery. The two batteries are both made by GS Yuasa Corp., which is based in the city of Kyoto.
CT scan analyses continued to be carried out on the main battery of the ANA jet at a Tokyo facility of the Japan Aerospace Exploration Agency.
After finishing the analysis of the charred battery, it will be sent to GS Yuasa for scrutiny, the safety board said.
Together with inspectors of the NTSB, officials of Thales SA, a French military aircraft builder that designed the 787 electrical system, also observed the analysis at the request of French aviation safety authorities.
The Land, Infrastructure, Transport and Tourism Ministry and the U.S. Federal Aviation Administration meanwhile continued their investigation into GS Yuasa for a third straight day.